Conventionally, there is an electromagnetic opening/closing device, which is disclosed in the following Patent literature 1 for example. In the electromagnetic opening/closing device described in the Patent literature 1, a relay unit (electromagnetic relay) is housed within a casing made of synthetic resin, and a pair of main terminals and a pair of coil terminals are located so as to project at the casing. In this case, the pair of main terminals is connected to a contact of the relay unit, and a pair of coil terminals is connected to a coil used for an electromagnet of the relay unit. Further, the pair of main terminals is connected to a power-feeding path through which the electric power is supplied from an electric power source to a load. While excitation current flows between the pair of coil terminals, the relay unit (electromagnetic opening/closing device) turns on. While no excitation current flows between the pair of coil terminals, the relay unit (electromagnetic opening/closing device) turns off. That is, the power-feeding path from the electric power source to the load is closed, when the electromagnetic opening/closing device turns on, and is opened, when the electromagnetic opening/closing device turns off.